Connector system with physical security feature

ABSTRACT

A connector system comprising a set of plug housings, each plug housing having a front face and defining a first keying element at least partially on the front face, the first keying element of each plug housing in the set of plug housings being different, a set of receptacles, each receptacle being an adapter configured to connect two plugs together, each receptacle defining a front opening and a second keying element projecting from at least one interior surface of the receptacle into the front interior space of the receptacle, the second keying element of the each receptacle of the set of receptacles being different and being adapted to cooperate with the first keying element of one and only one plug housing of the set of plug housings such that each receptacle of the set of receptacles mates with only one plug housing of the set of plug housings.

CROSS REFERENCE TO RELATED APPLICATIONS

This present application is a continuation of application Ser. No.13/839,732, filed Mar. 15, 2013, and a continuation of application Ser.No. 13/447,613, filed Apr. 16, 2012, and a continuation of applicationSer. No. 12/876,943, filed Sep. 7, 2010; which is a continuation-in-partof application Ser. No. 12/061,064, filed Apr. 2, 2008, now U.S. Pat.No. 7,789,572; which is a continuation-in-part of application Ser. No.11/930,751, filed Oct. 31, 2007, now U.S. Pat. No. 7,651,277; which is adivisional of application Ser. No. 11/254,356, filed Oct. 20, 2005, nowU.S. Pat. No. 7,325,976; which is a continuation-in-part of applicationSer. No. 10/982,374, filed Nov. 5, 2004, now U.S. Pat. No. 7,207,724,and a continuation-in-part of application Ser. No. 09/908,140, filedJul. 17, 2001, now U.S. Pat. No. 6,960,025, which claims benefit ofProvisional Application No. 60/218,705, filed Jul. 17, 2000. Theapplication hereby claims priority to all of the aforementionedapplications, which are also all hereby incorporated by reference intheir entirety.

FIELD OF INVENTION

The present invention relates generally to connectors for use intelecommunication networks such as voice, data or video networks. Morespecifically, to a connector system in which only certain plugs can matewith certain receptacles to provide discriminating access to particularinformation networks.

BACKGROUND

A need has developed to limit user access in data networks for securityor other purposes. In recent years, buildings/offices are being equippedwith different information networks, each having access to differentdata. It is important to restrict access to these networks to onlyauthorized users. While some restrictions may be achieved using softwareapproaches, such as passwords, the applicants have identified the needto restrict access further using some type of “physical barrier” to thenetworks. The present invention fulfills this need among others.

SUMMARY OF INVENTION

The following presents a simplified summary of the invention in order toprovide a basic understanding of some aspects of the invention. Thissummary is not an extensive overview of the invention. It is notintended to identify key/critical elements of the invention or todelineate the scope of the invention. Its sole purpose is to presentsome concepts of the invention in a simplified form as a prelude to themore detailed description that is presented later.

The present invention provides a connector system which uses physicalbarriers to prevent unauthorized users from connecting to data networks.More specifically, the applicants recognize that the best protectionagainst unauthorized users “hacking” into data networks containingconfidential information is to prevent them from even connecting to thenetwork. This can be accomplished using physical barriers which preventplugs from mating with receptacles. To this end, the present inventionfacilitates discriminating mating among similar, but different, plugsand receptacles by using a system of geometrically matched connectorcomponents which allows certain combinations of plugs andreceptacles—i.e., mating pairs—to mate, while preventing othercombinations from mating. Thus, the connector system of the presentinvention imparts physical security to a particular data network byensuring that only authorized users who possess a particular connectorcomponent can physically connect to the particular data network.

In a preferred embodiment, the network comprises: (a) a set of opticalplugs, each plug having a housing and a ferrule, the housing having afront and back orientation and having a front face defining an opening,the ferrule being disposed within the opening, the housing defining afirst keying element on the front face around the opening, the keyingelement for each optical plug of the set of optical plugs beingdifferent; and (b) a set of optical receptacles, each receptacle havingan opening to receive the plug and a ferrule-receiving portion toreceive the ferrule, the ferrule-receiving portion defining a secondkeying element to cooperate with the first keying element, the secondkeying element for each receptacle of the set of the optical receptaclesbeing different and being adapted to cooperate with one and only one ofthe first keying elements, wherein plugs and receptacles having keyingelements that cooperate are mating pairs.

Having the keying element located on the face of the plug provides for anumber of benefits. First, these features can be molded with arelatively small change to the mold dies. Specifically, the openingaround the ferrule is typically defined in the molding process by a corepin which is inserted into the outer mold. Changing core pinconfigurations is a relatively inexpensive and easy step compared toaltering the configuration of the outer molds. Therefore, as mentionedabove, the connector system of the present invention provides for avariety of different plug configurations with only slight modificationsto the molding process.

Having the security features on the front face of the plug also providesfor an early indication of non-mateability. Specifically, since thefeatures are located on essentially the leading edge of the plug, theyare positioned optimally to “stub” as soon as possible when a plug isinserted into a non-mating receptacle. The applicants recognize thatinterference between connector components which are non-mating should bemade as soon as possible to minimize the possibility of coupling lightbetween connectors. That is, if close enough, optical connectors areable to couple, albeit with high loss, even if the connectors are notmechanically engaged. This condition can be meliorated by preventing thelight carrying elements from getting too close—hence the desire to stubearly. Stubbing early also provides an early signal to the user that theplug is non-mating and avoids the tendency of trying to force a pluginto a non-mating receptacle.

Additionally, by locating the keying feature on the leading surface ofthe plug, the corresponding keying feature on the receptacle may belocated internally and still provide an early indication ofnon-mateability. This is beneficial since it is desirable to locate thekeying feature of the receptacle internally to minimize the ability ofthe keying feature to be tampered with or otherwise overridden. Asdiscussed below, this is of particular importance in the configurationof the MT-RJ and LC connectors in which the plug defines the slot andthe receptacle defines the key. If the key is removed, the securityfeature is breached. Having the key located within the receptaclereduces this risk.

Yet another benefit of having the keying features located on the frontface of the plug is the visual indication the plug provides with respectto its keying features. That is, one can readily determine the keyingconfiguration of the plug by visual inspection of its front face. Thereis no need to look into an opening to inspect the internal geometry ofthe plug to determine its keying configuration.

Another aspect of the present invention is an economical process forproducing the plugs by altering their geometry at their front end thougha simple mold modification. In a preferred embodiment, the processcomprises: (a) molding a first housing for a first plug of a set ofplugs using a core pin to define an opening having a first keyingelement in a first position; and (b) molding a second housing for asecond plug of the set of plugs by adjusting only the core pin to definethe opening having a first keying element in a second position differentthan the first position.

Yet another embodiment of the present invention is a multi-connectorassembly in which two or more of the connectors have different securefeatures. In one embodiment, the connector system comprising amulti-plug connector, each plug having a housing and a ferrule, thehousing having a front and back orientation and having a front facedefining an opening, the ferrule being disposed within the opening, thehousing defining a first keying element on the front face around theopening, at least two housings of the multi-plug connector havingdifferent the first keying elements.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a mating pair of the present invention in which a plug isbeing inserted into a receptacle.

FIG. 2 shows a non-mating pair in which a plug has a slot which is notin the proper position to accept a key of a receptacle.

FIG. 3 shows an end view of a first plug showing a first keying element(a slot) in a first position to accept a second keying element (a key)of a first mating receptacle as shown in FIG. 4. FIG. 3A shows an endview of second plug with a first keying element (a slot) in a secondposition which accepts a second keying element (a key) of a secondmating receptacle as shown in FIG. 4 a.

FIG. 4 shows an end view of the first receptacle having a second keyingelement (a key) in a first position to accept a first keying element ofthe first plug shown in FIG. 3 to form a first mating pair. FIG. 4 ashows an end view of the second receptacle having a second keyingelement (a key) in a second position to accept a first keying element ofthe second plug in FIG. 3 a to form a second mating pair.

FIG. 5 shows a plug having a slot configuration capable of mating withjacks having keys in different positions.

FIGS. 6( a)-6(c) show top perspective, front and rear views,respectively, of an MT-RJ connector plug having security features of thepresent invention.

FIGS. 7( a) and 7(b) show top perspective and front views, respectively,of an MT-RJ connector receptacle.

FIG. 8 shows a front and side perspective view of an LC connector plughaving security features of the present invention.

FIG. 9 shows a front perspective view of an LC connector receptaclehaving security features of the present invention.

FIG. 10 shows schematically the discrete positions available for thefirst keying element.

FIG. 11 shows a series of LC connector plugs in which the firstgeometries are different.

FIG. 12 shows a hybrid adapter.

FIGS. 13( a) and (b) show duplex and quad connectors having receptacleswith the same security features.

FIGS. 14( a) and (b) show duplex and quad connectors having receptacleswith different security features.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention relates to a connector system comprising a seriesof connector components which interconnect with each other in adiscretionary way. Referring to FIG. 1, a preferred embodiment of amating plug 101 and receptacle 100 of the connector system isillustrated. As shown, the plug 101 is partially inserted into thereceptacle 100, which, in this embodiment, is a jack having a tubportion 102. Although a jack is discussed herein in detail, it should beunderstood that the receptacle of the present invention is notrestricted to a jack and may be any structure configured to receive aplug, including, for example, an adapter for connecting two plugstogether or an integral connector on an active device (e.g.,transceiver) or passive device (e.g., splitter).

The plug typically contains a conductive element, such a fiber or wire,which mates with a similar element in the receptacle. In fiber opticapplications, it is common for the conductive element to be contained ina ferrule 150, which in turn is housed by the plug 101 as shown inFIG. 1. In a preferred embodiment, the ferrule is an MT-type ferrule,which as known, is rectangular having side surfaces 151, 152, a bottomsurface 153 and a top surface t not shown).

The outer surface of the plug 101 and the inner surface of the tub 102have first and second geometries, respectively, which cooperate to allowonly certain pairs of plugs and receptacles to mate (herein “matingpairs,” “mating plug and jack,” or “keyed pair”), and which physicallyinterfere for all other combinations of plugs and jacks (herein“non-mating pairs,” “non-mating plugs and jack,” or “non-keyed pairs”),thereby preventing non-mating plugs and jacks from effecting an opticalor electrical coupling.

The first and second geometries may embody any known keying mechanismwhich discriminates between connector components. Such keying mechanismsinclude, for example, a key and slot relationship between the plug andjack, a receptacle dimensioned to receive only certain sized or shapedplugs, and even a magnetic signature for either attracting (for matingpairs) and repulsing (non-mating pairs). Preferably, the keyingmechanism involves just a slight modification to the plug and jack suchthat essentially the same molds can be used to manufacture connectors ofdifferent keyed pairs. Although molding is preferred, it is should beunderstood that other techniques for producing the first and secondgeometries can be used including, for example, over molding andmachining.

In a preferred embodiment, the invention uses a key and slot mechanism.For simplicity, the term “keying elements” refers collectively to thekey and the slot. Specifically, the slot can be embodied in the first orsecond geometry and the key can be embodied in the other geometry. Inthe particularly preferred embodiment shown in FIGS. 1-4, the key ispart of the second geometry, while the slot is part of the firstgeometry; that is, the plug 101 has a slot 103 and the tub portion 102of the jack has a key 104.

This configuration is preferred since the key may cooperate with other“ribs” on the connector for pre-alignment purposes. More specifically,with particular reference to FIG. 3, an end view of housing 301 of theplug 101 is shown. The housing comprises four walls each wall having aslot 103, 302 a, 302 h, and 302 c. respectively. FIG. 4 depicts an endview of housing 401 of the tub 400 in which the key 104 and ribs 402 a,402 b, and 402 c are disposed on the walls of the housing. The key 104and the ribs 402 a, 402 b, and 402 c cooperate with the slots 103, 302,302 a, 302 b, and 302 c, respectively, to effect pre-alignment of theferrule located within the plug with the jack before final mating of theconnector plug with the connector jack. The final mating may be betweenthe conductive elements of the connector system, such as, for example,between a couple of MT-type ferrules, which employ precise alignmentpins/receiving holes on the ferrule face. Such ferrules are well knownin the art. By pre-aligning the MT ferrules through the synergistic useof the key and slot, the inter-engagement of the closely-tolerancedalignment pins/receiving holes is facilitated. The above-describedsynergistic keying and aligning feature of the present invention isrealized with the MT-RJ connector (Tyco Electronics, Harrisburg, PA).

In a preferred embodiment, the mating end of the key 104 contains a flatportion shown as 105 and the mating end of the plug 101 has a chamfers106 on the corners of the edges of the slot 103, while the remainder ofthe mating end of the plug comprises a flat portion 107. The radiuscorners on the key 106 and the chamfers on the plug 101 work as aguiding device and provide for the necessary alignment between the keyand the slot when the plug is inserted into the tub of the jack. On theother hand, as shown in FIG. 2, when a user attempts to mate twonon-mating plug and jack components, the flat portion of the key 105contacts the flat portion of the plug 101 and provides for definitephysical interference between the plug and jack when the slot and key donot correspond. Accordingly, the use of this geometry prevents a userfrom forcing two non-mating plugs and jacks together. Therefore, thephysical interference provided between the flat portion 105 of the tuband the flat portion 107 of the key assures that only desiredcombinations of plugs and jacks will mate.

The position of the key 104 on the tub 102 and the slot 103 on the plug101 can be varied in such a manner so that a plurality ofmutually-exclusive slot and key positions are formed. in one embodiment,the series of key and slot locations are mutually exclusive so thatthere is a one-to-one correspondence between jacks and plugs. In anotherembodiment, certain plugs may be configured to mate with a variety ofdifferent jacks. For example, it may be worthwhile to give networkadministers or people with high security clearance certain “master”plugs which are capable of mating with a number of jacks havingdifferent slot positions. Referring to the figures, FIG. 5 shows anembodiment of a master plug 501 which has a slot 502 that is configured(which, in this embodiment, means it is wide enough) to mate with jacks503 and 504 which have different key positions 505 and 506,respectively. Although a wide slot is used in this embodiment to effectmating with two or more jacks having different key configurations, itshould be understood that other embodiments are possible, such as, forexample a plug with two or more slots.

The number of possible mutually exclusive mating pairs for a given plugand receptacle is a function of the physical parameters of the plug andthe receptacle. More specifically, with reference to FIGS. 1-4, mutualexclusivity is ensured by adhering to the following relationships:X1−C/2+(D−A)+Δ<=F/2  (1)X2+B/2<A/2−W  (2)X1a+Clear1+Z=X1b  (3)

wherein:

-   -   A=the width of the plug 101;    -   B=the width of the slot 103 on the plug 101;    -   C=the width of the key 104;    -   D=the distance across the opening of the tub;    -   F=the width of the ferrule residing within the plug;    -   Δ=CLF−CLA, wherein        -   CLA=centerline of the width of the plug; and        -   CLF=centerline of the ferrule residing within the plug.    -   X1=the distance from the center of the opening in the tub 102 to        the center of the key 104 for each mutually exclusive position.    -   X2=the distance from the center of the plug 101 to the center of        the slot 103 for each mutually exclusive position;    -   X1a=the X1 distance for a sequentially first key in a series of        connectors;    -   X1b=the X1 distance for a sequentially second key in a series of        connectors;    -   W=the wall thickness of the plug housing    -   Z=the minimum distance required to ensure that the flat portion        of the key does not contact the flat portion of the plug 107        when a user attempts to mate a mating pair;    -   Clear1=the clearance distance between the center side of the key        and the center side of the slot.

These relationships must be satisfied for the mating pairs to mate andfor the non-mating pairs to definitely not mate. Specifically, for amating pair, Relationship (1) requires that half the ferrule width mustbe no less than X₁ less one half of C added to the difference betweenthe width of the tub opening D less the width of the plug added to thedifference between the centerline of the ferrule within the plug and thecenterline of the plug. This ensures that the key is not positionedoutside of the area on which at least a portion of the ferrule willreside. By adhering to this parameter, the key will have some overlapwith the ferrule, and thus will provide for pre-alignment of the ferrulein the same manner as do the ribs on the three sides of the ferrulewithout the key.

Relationship (2) requires that X₂ added to one-half of dimension B isless than one-half of dimension A less W. This assures that the slotresides on the plug within the confines of the plug walls.

Finally, according to Relationship (3), for each mutually exclusiveposition, the distance X₁ for the first connector in the system (X_(1a))added to Clear₁ added to a predefined interference interval Z wouldcorrespond to the distance X₁ for the next slot/key position (X_(1b)). Zis the minimum distance required to ensure that the flat portion of thekey does not contact the flat portion of the plug 107 when a userattempts to mate the two portions of a connecter which is intended tomate.

By way of example, four mutually exclusive locations for locating theslot on the plug housing and the key on the tub are defined below for anMT-RJ connector. The MT-RJ connector has the following dimensions:

-   -   A=7.15±        05 mm    -   B=1.25 mm    -   C=0.95±        04 mm    -   D=7.24±0.04 mm    -   F=4.5±        04 mm    -   Clear1=0.15 mm    -   W=0.8 mm

Based on these MT-RJ dimensions, it has been found that the following X₁key positions satisfy the relationships above:

Mating pair Key Position X₁ 1 1 0.8 mm 2 2 1.6 mm 3 3 −0.8 mm  4 4 −1.6mm 

For example, FIG. 3 shows an end view of a first plug housing 301showing a first keying element 103 (a slot) in a first X₁ position toaccept a second keying element 104 (a key) of a first receptacle housing401 as shown in FIG. 4. FIG. 4 shows an end view of the first receptaclehousing 401 having a ferrule-receiving portion having a second keyingelement 104 (a key) in a first X₁ position to accept a first keyingelement 103 of the first plug housing 103 shown in FIG. 3 to form afirst mating pair. FIG. 3A shows an end view of second plug housing 301a with a first keying element 103 a (a slot) in a second X₁ positionwhich accepts a second keying element 104 a (a key) of a secondreceptacle housing 401 a as shown in FIG. 4A. FIG. 4A shows an end viewof the second receptacle housing 401 having ferrule-receiving portion450 having a second keying element 104 a (a key) in a second X₁ positionto accept a first keying element 103 a of the second plug housing 301 ashown in FIG. 3A to form a second mating pair.

Although the data above indicates four mutually exclusive positions, itshould be understood that additional positions are possible within theparameters of the MT-RJ connector. Additionally, it should be understoodthat the combinations of various key positions can be used to increasethe number of permutations of mating pairs. For example, in addition tothe four mating pairs listed above, additional mating pairconfigurations may obtained from the following combinations of keypositions:

Mating pair Key Positions 5 1, 2 6 1, 2, 3 7 1, 2, 3, 4 8 2, 3 9 2, 4 102, 3, 4 11 3, 4 12 1, 3 13 1, 4 14 1, 3, 4 15 1, 2, 4

In a preferred embodiment, the key and slot components are combined withthe industry standard MT-RJ connector. FIG. 6 and FIG. 7 show thekey-slot combination added to the MT-RJ connector as produced by TycoElectronics of Harrisburg, Pa.

FIGS. 6( a)-(c) show the plug 602 of the MT-RJ connector combined withthe slot 601 of the present invention. FIGS. 7( a) and 7(b) show thecenter tub portion 703 of an MT-RJ connector jack. The key is shown as701 located in one of the plurality of possible positions. The threepre-alignment ribs are shown as 702 a, 702 b, and 702 c. The key 701functions as the discriminating member for allowing or preventing matingwith a plurality of plugs, while at the same time functioning as thepre-alignment member for the remaining side of the ferrule not alignedwith ribs 702 a, 702 b, and 702 c.

To provide a simple and readily apparent indication to the user of whichplugs mate with which receptacles, it is preferable to mark mating pairswith indicia or color to indicate their compatibility. In a preferredembodiment, the components of a mating pair are a similar colordifferent from all others used in the connector system.

Referring to FIGS. 8 & 9, another embodiment of the connector system ofthe present invention is shown. FIG. 8 shows a plug 800, which is one ofa set of different plugs in the system. Each plug has a housing 801which defines a first geometry. The first geometry comprises a frontface 804 with an opening 802 (demarcated with dotted line), and aferrule (not shown) within said housing and disposed in said opening.Around said opening 802 is a first keying element 803. The keyingelement for each different optical plug of said set of optical plugs isdifferent.

FIG. 9 shows a receptacle 900 for receiving a particular plug (notshown) and is one of a set of different receptacles. The receptacle 900has a second geometry configured to receive the first geometry of aplug. The second geometry comprises a cavity 901 to receive a plug and aferrule-receiving portion 904 having a borehole 902 to receive theferrule of the plug. The ferrule-receiving portion 904 defines a secondkeying element 903 to cooperate with a first keying element of aparticular plug. The second keying element for each receptacle of saidset of said optical receptacles is different and is adapted to cooperatewith one and only one first keying element. Plugs and receptacles havingkeying elements that cooperate are referred to herein as “mating pairs.”

Although the LC connector system described above is a single-fiberferrule rather than a multifiber ferrule, the general keying featuresare essentially the same as those described above with respect to theMT-RJ connector. Further, the keying features of the plug 800 andreceptacle 900 of the present invention may be implemented in any wellknown optical connector including, for example, other single-fiberferrule connectors such as MU, SC, ST, or FC connectors. Forillustrative purposes, the security features are described with respectto the LC connector system, which includes the LC plug (plug 800) and LCadapter (receptacle 900). Aside from the security features describedherein, these connector components are the same as those specified inthe LC Standard available on-line or from OFS (Japan), and the commonfeatures between them will not be addressed herein.

Like the MT-RJ embodiment described above, the keying features of the LCconnector are contained on the front face of the plug. This is importantfor a number of reasons. First, these features can be molded with arelatively small change to the mold dies. Specifically, the openingaround the ferrule is typically defined in the molding process by a corepin which is inserted into the outer mold. Changing core pinconfigurations is a relatively inexpensive and easy step compared toaltering the configuration of the outer molds. Therefore, as mentionedabove, the connector system of the present invention provides for avariety of different plug configurations with only slight modificationsto the molding process.

Having the security features on the front face of the plug also providesfor an early indication of non-matability. Specifically, since thefeatures are located on essentially the leading edge of the plug, theyare positioned optimally to “stub” as soon as possible when a plug isinserted into a non-mating receptacle. The applicants recognize thatinterference between connector components which are non-mating should bemade as soon as possible to minimize the possibility of coupling lightbetween connectors. That is, if close enough, optical connectors areable to couple, albeit with high loss, even if the connectors are notmechanically engaged. This condition can be meliorated by preventing thelight carrying elements from getting too close—hence the desire to stubearly. Stubbing early also provides an early signal to the user that theplug is non-mating and avoids the tendency of trying to force a pluginto a non-mating receptacle.

Additionally, by locating the keying feature on the leading surface ofthe plug, the corresponding keying feature on the receptacle may belocated internally and still provide an early indication ofnon-matability. This is beneficial since it is desirable to locate thekeying feature of the receptacle internally to minimize the ability ofthe keying feature to be tampered with or otherwise overridden. Asdiscussed below, this is of particular importance in the configurationof the MT-RJ and LC connectors in which the plug defines the slot andthe receptacle defines the key. If the key is removed, the securityfeature is breached. Having the key located within the receptaclereduces this risk.

Yet another benefit of having the keying features located on the frontface of the plug is the visual indication the plug provides with respectto its keying features. That is, one can readily determine the keyingconfiguration of the plug by visual inspection of its front face. Thereis no need to look into an opening to inspect the internal geometry ofthe plug to determine its keying configuration.

The keying elements that may be used in the LC connector are the same asthose described above with respect to the MT-RJ embodiment. In apreferred embodiment, the keying elements comprise a slot and a key. Theslot can be embodied in the first or second geometry and the key can beembodied in the other geometry. In a first configuration, the slot isembodied in the first geometry and the key is embodied in the secondgeometry, while in a second configuration, the key is embodied in thefirst geometry and the slot is embodied in the second geometry.

The LC connector shown in FIGS. 8-9 has a first configuration. Thisconfiguration is advantageous for a number of reasons. First, the firstkeying features do not prevent a plug from mating with an ordinaryreceptacle. This is particularly beneficial since a plug with keyingelements can be nevertheless “mated” with standard equipment used forthe polishing, testing and inspection of the ferrule. Specifically, thepolishing, testing and inspection equipment for single fiber ferrulestypically comprises a ferrule receiving interface, similar to that of areceptacle, which receives just the ferrule disposed in the opening ofthe housing. The housing is not engaged. If a key protrudes into thespace between the opening and the ferrule, it would preclude couplingwith this existing equipment. Conversely, by having slots extendradially outward from the opening, and thereby maintain the spacebetween the opening and the ferrule, a standard ferrule receivinginterface, which does not have keying features, can be used. Forexample, a plug having a first keying element can be coupled to astandard LC ferrule receiving interface connected to a polishing devicefor polishing the ferrule, or to a microscope for inspecting the endfacegeometry of the ferrule, or to a photodetector for testing opticalattenuation of the ferrule assembly.

Furthermore, since the physical “barrier”—i.e., the key—is located onthe receptacle in the first configuration, it will serve to facilitatediscriminatory mating among, not only plugs employing security features,but also existing plugs which have no security features of the presentinvention. Specifically, if a slot in the plug is necessary toaccommodate the key of the receptacle, then plugs without slots will notmate with receptacles having the key. Therefore, ordinary, non-securetype plugs which do not have the slot in the proper position will notmate with the receptacle. In contrast, a non-secure receptacle will matewith a secure plug of the first configuration. Specifically, since thephysical barrier is absent from the receptacle, any ordinary or secureplug can mate with it. As discussed below, the situation with the secondconfiguration is opposite from that of the first, meaning that a secureplug cannot mate with a non-secure receptacle but a secure receptaclecan mate with a non-secure plug. To provide for discrimination betweensecure and non-secure connectors components, a secondary key is added tothe system as discussed below.

A connector system having the second configuration offers certainbenefits, but also presents certain challenges. One benefit is that thespace consuming security feature—i.e., the slot—resides in thereceptacle which is typically larger than the plug and better suited foraccommodating this feature. That is, since a slot is defined by thematerial around it, a slot requires more room than a key. The receptacledoes not have the same space constraints as a plug (which is designed tobe inserted in the receptacle) and may be more capable of accommodatingthe slot than the plug. Additionally, it may be preferable to have one“master” plug which plugs into all receptacles having security features.This is easily accomplished with a connector system of the secondconfiguration. Specifically, the master plug would simply be one havingno key to interfere with the first geometry of the receptacle. Thesimplicity in offering a master plug in the connector system of thesecond configuration also gives rise to a challenge facing thesystem—the ability of non-secure plugs to mate with secure receptacles(discussed below).

Referring to FIG. 10, a preferred embodiment of the first keying element803 is shown schematically. The figure shows the opening 802 in whichthe ferrule is disposed and which is configured to receive theferrule-receiving portion 904. Positioned around the opening 802 arespatially discrete positions 101(a)-(h) for the first keying element.Similar discrete positions exist around the ferrule-receiving portion904 (see FIG. 9) to define the location of the second keying element. Ina preferred embodiment, the first keying element comprises one or moreslots in a combination of positions 101(a)-(h) and the second keyingelement comprises keys in corresponding positions. It should beunderstood that to facilitate cooperation between the first and secondkeying elements, the combination of slot positions in the plug must bethe same as the combination of key positions in the ferrule receivingportion 904. In other words, each slot must correspond to a key in thesame relative position to facilitate a mating pair. For example, a plughaving a first keying element which comprises slots in positions 1001 a,1001 d, 1001 e, and 1001 d, will mate with a receptacle having a secondkeying element comprising keys 905, 906, 907, and 908 is the samerelative positions (see FIG. 9).

The number of slots in the combination of first keying elements dependsupon the number of possible positions of the slots. Specifically, thenumber of possible permeations of different mating pairs is given by thefollowing equation:

${nCr} = \frac{n!}{{r!} \cdot {\left( {n - r} \right)!}}$

-   -   wherein:    -   n equals the number of spatially discrete positions for the        keying elements, and    -   r is the number of positions occupied.        _(n)C_(r) therefore provides for the number of mutually        exclusive combinations or permeations of mating pairs.

Below is a table providing data on the theoretical number of matingpairs, _(n)C_(r), for different n and r values.

Number of Spatially Number of Number of Mutually Discrete PositionsPositions Occupied Exclusive Combinations n r _(n)C_(r) 4 1 4 2 6 3 4 41 5 1 5 2 10 3 10 4 5 5 1 6 1 6 2 15 3 20 4 15 5 6 6 1

From this data, it is clear that the maximum number of permutations(i.e., _(n)C_(r)) is reached when the number of positions occupiedequals n divided by 2. Therefore, in the preferred embodiment, eithern/2 slots (if n is an even integer) or (n±1)/2 slots (if n is an oddinteger) of spatially discrete positions are occupied by either a slotwith respect to the plug or a key with respect to the receptacle. (Forpurposes of simplicity, hereinafter, n will be presumed to be an evennumber.) Therefore, using the equation above, the embodiment shown inFIGS. 8, 9 and 10, in which n equals 8 and r equals 4, the maximumnumber of permutations of mating pairs is 70.

Referring to FIG. 11, different of plugs 1101-1110 of a set are shown inwhich the first keying elements comprise slots in different combinationsof positions as defined in FIG. 10 and accompanying text. In thesedrawings, the opening 802 which is constant in all the plugs and theslot positions are shown with a phantom line. Specifically, plug 1101shows slots in a combination of positions 1001 c, 1001 d, 1001 e, and1001 f; plug 1102 shows slots in a combination of positions 1001 e, 1001f, 1001 g, and 1001 h; plug 1103 shows slots in a combination ofpositions 1001 a, 1001 b, 1001 g, and 1001 h; plug 1104 shows slots in acombination of positions 1001 a, 1001 b, 1001 c, and 1001 d; plug 1105shows slots in a combination of positions 1001 b, 1001 d, 1001 e, and1001 g; plug 1106 shows slots in a combination of positions 1001 b, 1001e, 1001 e, and 1001 h; plug 1107 shows slots in a combination ofpositions 1001 a, 1001 c, 1001 f, and 1001 h; plug 1108 shows slots in acombination of positions 1001 a, 1001 d, 1001 f, and 1001 g; plug 1109shows slots in a combination of positions 1001 a, 1001 d, 1001 e, and1001 h; and plug 1110 shows slots in a combination of positions 1001 b,1001 e, 1001 f, and 1001 g. It should be understood that each of theplugs described above will mate with a receptacle having a key in thesame position. For example, plug 1109 will mate with receptacle 900which has keys 904, 905, 906 and 907 in the same positions as the slots(i.e., 1001 a, 1001 d, 1001 e, and 1001 h).

In a preferred embodiment, the connector system of the present inventionmay contain one or more master plugs of varying levels. That is, theremay be lower-level master plugs, which can mate with receptacles of twodifferent networks, or higher-level master plugs, which can mate withreceptacles of three or more networks. The difference in the level ofthe mater plug is a function of the r number of slots occupying npossible positions—the more slots there are, the higher the plug'slevel. Specifically, the master plug comprises a first keying elementhaving a third combination of greater than n/2 slots, in which the slotsoccupy the positions of at least two different first combinations asdescribed above. Higher level master plugs have slots which occupy thepositions of three or more different first combinations.

Aside from showing the different combinations of keying elements, FIG.11 illustrates the ease with which the various plugs can be made.Specifically, in a preferred embodiment, the process of manufacturing anoptical connector comprises molding different plugs by adjusting thecore pin which defines the opening 802 while leaving the outer moldsessentially the same. In other words, rather than using different moldsto modify the outside of the housing—which can be expensive, the presentinvention involves simply adjusting the core pin—which is relativelyinexpensive. Referring to FIG. 11, the process is described in greaterdetail. The process comprises first molding a first housing 1101 a for afirst plug 1101 of a set of plugs 1101-1110 using a core pin (not shown)to define an opening 802 and a first keying element in a firstcombination of positions 1001 c, 1001 d, 1001 e, and 1001 f. Next, asecond housing 1102 a for a second plug 1102 is molded by adjusting onlysaid core pin to define first keying element in a second combination ofpositions 1001 e, 1101 f, 1001 g, and 1101 h, which is different fromfirst combination of positions.

To effect the different combinations of positions, the core pin ispreferably adjusted by rotating it in θ increments, in which 0 is equalto 360°/m, wherein m is an integer. Preferably m is an integer from2-18, more preferably from 2-5, and even more preferably from 3-4. Inthe embodiment shown in FIG. 10, m is 4, thus the core pin is adjustedby rotating it in 90° increments. It should be clear that rotating thiscore pin in 90° increments in subsequent molding operations will produceplugs 1103 and 1104, respectively. Plugs 1105-1108 were prepared using adifferent core pin which was also rotated in 90° increments. Plugs 1109and 1110 were prepared using yet a different core pin which was rotatedin a 90° increment. It is worthwhile to mention that since thecombination of positions 1001 b, 1001 c, 1001 f, and 1001 g issymmetrical with respect to two axes, the core pin can only be rotatedby one 90° increment before repeating the same combination of positions.

Once the housings are prepared, a ferrule is disposed in the opening ofeach housing to form a subassembly. A fiber may be terminated in theferrule either before or after the preparation of the subassembly. Forfield-terminatable connectors, it may be preferable to dispose just afiber stub in the ferrule. This configuration facilitates fieldinstallation of a fiber as discussed, for example, in WO2005004285.Regardless of whether a stub or a fiber is terminated in the ferrule,the preferred keying arrangement of the present invention in which slotsradiate outwardly from the opening 802 allows the subassembly of the LCconnector to be polished, inspected, and tested using standard polishingequipment as mentioned above.

An advantage of the connector system of the present invention is thatdifferent receptacles may be combined to form “hybrid” adapters. Morespecifically, aside from the second keying element extending outwardfrom the ferrule receiving portion, the receptacles are the same asthose used for standard connectors. This allows different receptacles tobe combined back to back to form hybrid adapters. In a particularlypreferred embodiment, a secure receptacle is combined with a nonsecurereceptacle by ultrasonically welding, or other known technique. Such aconfiguration is particularly useful in situations in which thenonsecure end of the adapter is located in an inherently secure area,for example, behind a wall or panel, where access is already limited. Inother words, since connectors within cabinets and walls cannot beaccessed readily after construction, the advantages derived from asecure connector at those ends would be minimal. Thus, it is preferableto use a nonsecure connector in these situations so the installer neednot concern himself with the “proper” secure connector configurationduring the installation of the infrastructure wiring.

To discriminate between secure and non-secure connector systems, thepresent invention provides for a secondary key & slot configuration,which is either non-existent or in a different position for all plugsand receptacles which are outside of the given connector system 800. Forexample, referring to FIG. 8, the first geometry comprises a secondaryplug 810, which is shown in the same relative position for all plugs ofa given set, but which may be in different positions as discussed below.Referring to FIG. 9, the second geometry of the geometry of thereceptacle comprises a secondary slot 910 are preferably, but notnecessarily, in the same position for all the receptacles of a given setof receptacles. The secondary slots 910 are adapted to receive secondarykeys 810. This way, only plugs and receptacles of a given set of havingaccommodating secondary keys/slots will mate. In a preferred embodiment,at least a portion of the secondary key 810 is disposed in the plug andis an extension of the side loading structure which is an LC connectorstandard. Therefore, in the preferred embodiment, the secondary key notonly provides for discriminating mating between secure and non-secureconnectors, but also enhances side load strength.

It is worthwhile to note that the use of the secondary key/slot addsanother security feature to the connector system—essentially anotherkeying mechanism. This additional keying feature increases the number ofpermutations within a given connector system. That is, rather thanmaintaining the same secondary key and slot location for all connectorswithin a system, it can be moved to form different classes within thesame family

Preferably, the keying elements (primary and secondary) are positionedsuch that not mating pairs “stub” at about the same axial positionrelative to one another regardless of whether the connectors areinterfering because they are different types of secure connectors orwhether they are interfering because they are secure/non-secureconnectors. This way, the user becomes accustomed to the point at whichnon-mating connector components interfere, thereby reducing the risk ofthe user forcing non-mating components together.

To provide a simple and readily apparent indication to the user of whichplugs mate with which receptacles, it is preferable to mark mating pairswith indicia or color to indicate their compatibility. In a preferredembodiment, the components of a mating pair are a similar colordifferent from all others used in the connector system.

The system described allows for a series of mutually-exclusiveconnectors to be used in a manner which provides physical security to anetwork system. In light of the often highly sensitive data stored onmany of the networks in use today, this is a highly desirable feature.The present invention is an effective way to segregate separate networksand assure that the proper users are connecting to the desired network.Additionally, the present invention may be employed in the manufactureof devices in which fibers or wires need to be connected in particulararrangements. More specifically, the discriminating connectors of thepresent invention can be engineered into a system such that, duringmanufacturing, the correct connection of the fibers/wires is ensured bythe mating pairs and their ability to prevent all other “incorrect”connections. Applications requiring particular routing of fibers orwires include, for example, routers, backplane assemblies, and evencomponent devices such as multiplexers/demultiplexers.

Considering, for example, routers/backplane assemblies, the connectorsystem of the present invention can be used to organize switch racksand, more specifically, to manage patch cables to reduce clutter andimprove the ease, reliability, and security of the patch cableinstallation by providing customer specific patch cables/backplaneconnections.

By way of background, although network architectures may vary, common tomost networks, and of particular interest herein, are switch racksystems. Such systems involve multiple-port switches mounted in a rack.Each activated port of a switch is connected to an aggregation box inthe panel with a patch cable. The aggregation box, in turn, is connectedto a deaggregation or breakout box with a trunk cable. The breakout boxbreaks out the trunk into individual channels again. Theinterconnections between the ports and the aggregation box and betweenthe aggregation and breakout boxes may be accomplished using opticalfiber or electrical conductor.

One of the objectives in designing switch racks is to minimize floorspace. To this end, efforts are generally concentrated on increasingport density. This means increasing the number of ports on a particularswitch and increasing the number of switches that fit into a particularrack or panel. A challenge in designing and installing such high portdensity switch racks is organizing the patch cables interconnecting theports to the aggregator. Each activated port requires a discreteconnection to the aggregator. This can lead to a great quantity of patchcables and general clutter, which creates a strong likelihood that apatch cable will be connected to the wrong port in error. Even trainedtechnicians find it difficult to work around such clutter effectivelyand without making errors. If a patch cable is in fact connected to thewrong port, it may take hours to troubleshoot and resolve the problem inthe mass of interconnections. Therefore, a need exists for a switch racksystem that reduces the likelihood of improper interconnections.

The connector system of the present system fulfills this need amongothers. Specifically, the patch cables may be configured with one ormore particular secure connectors to ensure that the correct plug isplugged into the correct receptacle. In one embodiment, theinterconnections are not only secure, but customized for a particularuser. Specifically, Applicants recognize that many of theinterconnections involve multi-connector assemblies such as duplex andquad connectors. Applicants also realized that the multi-connectorassemblies provide an opportunity to increase the number of permutationsof the secure connectors to the extent that particular duplex and quadconnector assemblies can be provided on a per customer basis.

By way of background, referring to FIGS. 13( a) and 13(b), oneembodiment of the invention is shown as a duplex and quad connectorshaving the same secure configuration for each connector. Specifically,the duplex connector 1301 has to two identical receptacles 1302, 1303,each having the same D-type configuration. (It should be apparent thatthis receptacle configuration corresponds to the plug 1101 shown in FIG.11.) Likewise, the quad connector 1304 shown in FIG. 13( b), comprisesfour identical receptacles 1305. (Again each receptacle corresponds tothe plug 1101 shown in FIG. 11.)

Although the connector embodiments of FIGS. 13( a) & (b) work well toensure a secure connection, they are limited in the number of uniqueconfigurations they can make. Specifically, referring to FIG. 13( a),the duplex connector 1301 with identical receptacles 1302 and 1303 onlyhas four unique combinations using the primary tooling. Likewise, thequad receptacle 1304 shown in FIG. 13( b) is also limited to just fourunique combinations using primary tooling. As used herein, the primarytooling refers to the tooling required to make embodiments 1101-1104 asshown in FIG. 11( b). As mentioned above, one of the advantages of theconnector system shown in FIG. 11, is the ability to provide differentreceptacle and plug configurations simply by rotating the core pin. Inother words, different configurations can be manufactured using the sametooling. This is desirable from a production cost standpoint.

Although the number of permutations of the quad shown in FIG. 13( b)could be increased to forty (40) by using the ten (10) alternativeconfigurations keying configuration illustrated in plugs 1101-1110 inFIG. 11, this requires additional tooling because plugs 1105-1110 cannotbe produced by rotating the core pin used in the manufacture of plugs1101-1104.

In addition to a desire to avoid additional tooling requirements,Applicants have identified a need to further increase the number ofunique connector combinations so that certain multi-connectorconfigurations can be customized for a particular user. To this end,Applicants disclose herein multi-connector assembly in which two or moreof the geometries of the connectors of a given assembly are different.For example, one embodiment of the duplex connector 1401 of the presentinvention is shown in FIG. 14( a). In this embodiment, the duplexconnector 1401 comprises one receptacle 1402 having a geometry similarto the receptacles shown in FIG. 13A, but its second receptacle 1403 hasa different geometry, corresponding to the plug 1103 shown in FIG. 11.By configuring the duplex connector 1401 such that at least two of thereceptacles have different first geometries, the number of uniquecombinations increases from four to sixteen.

Even more permutations can be derived from the quad connector 1404 asshown in FIG. 14( b). Specifically, quad connector 1404 can be arrangedsuch that at least two of the receptacles have different geometries. Asshown in FIG. 14B, quad 1404 has four receptacles 1405, 1406, 1407,1408, all of which have a different geometry. Specifically, 1405corresponds to plug 1101, receptacle 1406 corresponds to plug 1102,receptacle 1407 corresponds to plug 1104 and receptacle corresponds toplug 1103. It should be understood that while each of these isdifferent, the number of different plug/receptacle geometries can carryfrom two to four in this assembly. By altering the geometries within thequad connector, the number of unique permutations increasesdramatically. For example, just using the primary tooling describedabove, 256 combinations are possible. When all ten keying combinationsare used as shown in FIG. 11, 1600 unique combinations are possible.

In addition to increasing the number of unique connector assemblies,varying the geometry among the connectors of a given assembly alsoimproves the resilience of the connector to a “forced” connection.Specifically, when the geometries are aligned as they are in theconnectors of FIGS. 13( a) & (b), a user can force the connection bybiasing the mating connector to one side or the other. For example, if auser wanted to force a connection to the duplex connector 1301 of FIG.13( a), the user could urge the plug assembly to the left of the duplexconnector 1301 during mating. However, by varying the geometries as inthe embodiment of FIGS. 14( a) and (b) such that there is nopolarization or alignment of the geometries, a user can no longer urgethe mating connector to one side or the other to force the connection.Thus, the embodiments of FIGS. 14( a) and (b) are also less prone toforced connections.

It should be understood that specific plug assemblies such as a duplexand quad are not illustrated particularly herein, but that suchconnectors assemblies are produced by clipping together simplexconnectors, such as those shown in FIG. 11, with a known clip (see, forexample, U.S. Pat. No. 7,500,790, incorporated herein by reference.)

Because the present invention provides for so many unique combinations,it is possible to designate certain unique configurations for certaincustomers. In this regard, the color of the connector itself may be usedto render it unique for a certain customer. For example, the quadconnector embodiment shown in FIG. 14( b) may be provided in green forone customer and be provided in blue for a different customer. Thus, thephysical connectors themselves may be the same but the colors aredifferent based on the user.

In one embodiment, the housings are color coded as described above. Inanother embodiment, the connectors comprise strain relief bootsextending rearwardly (not shown) that are color coded to increase thenumber of color permutations possible. Such strain relief boots are wellknown and are disclosed, for example, in U.S. Pat. No. 7,695,197,incorporated herein by reference.

It should be understood that while the multiple connector configurationswere discussed in terms of a patch cords, the application is by no meanslimited to patch cord applications. Indeed, the unique multi-connectorarrangements can be applied in any situation requiring multi-connectorconnections. In this regard, it should be understood that the foregoingis illustrative and not limiting and that obvious modifications may bemade by those skilled in the art without departing from the spirit ofthe invention. Accordingly, the specification is intended to cover suchalternatives, modifications, and equivalence as may be included withinthe spirit and scope of the invention as defined in the followingclaims.

What is claimed:
 1. A connector system comprising: a set of plughousings, each plug housing having a front face, said each plug housingdefining a first keying element at least partially on said front face,said first keying element of said each plug housing in said set of plughousings being different; a set of receptacles, each receptacle of saidset of receptacles constituting a portion of an adapter for connectingtwo plugs together, said each receptacle defining a front opening and afront interior space to receive one of said plug housings, said eachreceptacle defining a second keying element projecting from at least oneinterior surface of said each receptacle into the front interior spaceof said each receptacle, said second keying element of said eachreceptacle of said set of receptacles being different and being adaptedto cooperate with said first keying element of one and only one plughousing of said set of plug housings such that said each receptacle ofsaid set of receptacles mates with only one plug housing of said set ofplug housings, wherein said each plug housing and said each receptaclehaving said first and second keying elements that cooperate is a matingpair; and wherein said each plug housing and said each receptacle ofsaid mating pair is marked with a matching visual identificationdifferent from plug housings and receptacles having different first andsecond keying elements.
 2. The connector system of claim 1, wherein saideach plug housings is an optical plug housing and said each receptacles,is an optical receptacle, and wherein said each receptacles furtherincludes a ferrule alignment portion that assists in positioning aferrule disposed in said each plug housing upon insertion of said eachplug housing into said each receptacle of said mating pair, and whereinfor said each receptacles, the second keying element is part of theferrule alignment portion.
 3. The connector system of claim 2, whereinthe ferrule alignment portion includes top and bottom surface portionsand left and right surface portions, wherein the top and bottom surfaceportions are spaced apart to permit insertion of said ferruletherebetween, and wherein the left and right surface portions are spacedapart to permit insertion of said ferrule therebetween, and wherein saidtop and bottom surface portions and said left and right surface portionsguide said ferrule toward a mating position upon insertion of said eachplug housing into said each receptacle of said mating pair.
 4. Theconnector system of claim 3, wherein said ferrule is rectangular, andwherein the top, bottom, left, and right surface portions arenon-contiguous and positioned and configured to pre-align therectangular ferrule upon insertion of said each plug housing into saideach receptacle of said mating pair.
 5. The connector system of claim 3,wherein the top, bottom, left, and right surface portions are each onone of four ribs respectively that extend into the front interior spacefrom a top, bottom, left, and right interior side wall surfacerespectively in said each receptacle.
 6. The connector system of claim1, wherein said each of the receptacles is an optical receptacle thatincludes a plurality of walls defining the front interior space, andwherein said each of the receptacles includes top and bottom surfaceportions and left and right surface portions positioned within the frontinterior space and inwardly from the plurality of walls, and whereinsaid each of the top, bottom, left and right surface portions align witha corresponding top, bottom, left and right surface portion of a ferrulerespectively upon insertion of said each plug housing into said eachreceptacle of said mating pair.
 7. The connector system of claim 6,wherein the top and bottom surface portions of said each receptacle areoffset from each other by a vertical distance, and wherein the left andright surface portions are separated by a horizontal distance greaterthan said vertical distance, and wherein the top, bottom, left and rightsurface portions are substantially flat.
 8. The connector system ofclaim 6, wherein the top, bottom, left, and right surface portions ofsaid each receptacle are each on one of four ribs respectively thatextend from top, bottom, left, and right interior side wall surfacesrespectively on each of said receptacles.
 9. The connector system ofclaim 2, wherein the ferrule alignment portion in said each receptacleincludes at least one radiused or chamfered corner to help guide saidferrule upon insertion of said each plug housing into said eachreceptacle of said mating pair.
 10. The connector system of claim 1,wherein said each receptacle is an optical receptacle, and wherein thesecond keying element on said each receptacle includes at least oneradiused or chamfered corner to help guide the ferrule upon insertion ofsaid each plug housing into said each receptacle of said mating pair.11. The connector system of claim 1, wherein said visual identificationis a color.
 12. The connector system of claim 1, wherein each receptacleincludes a plurality of walls defining said front interior space,wherein one of said plurality of walls is a back wall recessed from thefront opening, wherein the second keying element on said each receptacleextends from at least one of said plurality of walls.
 13. The connectorsystem of claim 12, wherein said each receptacle is an opticalreceptacle, and wherein said plurality of walls includes a first wall, asecond wall, a third wall and a fourth wall, and wherein said eachreceptacle includes a ferrule alignment portion, said ferrule alignmentportion including a first rib, a second rib, a third rib, and a fourthrib, said fourth rib being said second keying element, and wherein thefirst rib extends from the first wall, the second rib extends from thesecond wall, the third rib extends from the third wall, and the secondkeying element extends from the fourth wall.
 14. The connector system ofclaim 2, wherein said each plug housing has an inner periphery, andwherein said first keying element is defined at least in part on saidfront face and said inner periphery, and wherein, when said eachreceptacle and said each plug housing of said mating pair are in a matedstate, at least part of said ferrule alignment portion of said eachreceptacle is received in said front face of said each plug housing. 15.The connector system of claim 1, wherein said first keying element ofsaid each plug housings of said set of plug housings has substantiallythe same shape and is located at a predefined position, said predefinedposition of said first keying element for said each plug housing of saidset of plug housings being different, and wherein said second keyingelement of said each receptacle of said set of receptacles hassubstantially the same shape and is located at a predefined position,said predefined position of said second keying element for said eachreceptacle of said set of said receptacles being different.
 16. Aconnector set of discriminating receptacles and plugs, said connectorset comprising: a plurality of different receptacles and a plurality ofdifferent plugs for optically coupling with said different receptacles,each different plug having a unique first geometry, each differentreceptacle having a unique second geometry; wherein said unique firstgeometry corresponds to one, and only one, said unique second geometrysuch that said each different receptacle mates with only one of theplurality of different plugs, wherein said each different plug and saideach different receptacle having corresponding unique first and secondgeometries in said connector set are a mating pair; wherein each matingpair is marked with a matching visual identification different from saiddifferent plugs and different receptacles having different first andsecond geometries in said connector set; wherein said each differentplug has a plug housing front face, said unique first geometrycomprising a first keying element in a predefined position at leastpartially on said plug housing front face, said predefined position ofsaid first keying element being different for said each different plug;and wherein said each different receptacle has a front face defining afirst opening and an interior to receive a mating plug of said differentplug, said interior defined at least in part by a back wall having asecond opening therethrough, said second opening having a shape thatcorresponds to the shape of a ferrule disposed in said mating plug, saidunique second geometry comprising a second keying element in apredefined position within said interior and recessed from said frontface of said each different receptacle, said predefined position of saidsecond keying element being different for said each differentreceptacle.
 17. The connector set of claim 16, wherein the second keyingelement of said each different receptacle is at least a part of aprojection extending into said interior of said each differentreceptacle, and wherein the projection guides said ferrule in saidmating plug toward said second opening in said back wall as said matingplug is inserted into said each different receptacle.
 18. The connectorset of claim 16, wherein said plurality of different receptacles andsaid plurality of different plugs are MT-RJ type connectors.
 19. Theconnector system of claim 17, wherein the projection in said eachdifferent receptacle includes at least one radiused or chamfered cornerto help guide said ferrule inserted into said each different receptacle.20. The connector system of claim 16, wherein the second keying elementof said each different receptacle includes at least one radiused orchamfered corner to help guide said ferrule of said mating plug insertedinto said each different receptacle.
 21. The connector system of claim16, wherein at least one of said different receptacles is at least aportion of an adapter configured to connect two optical plugs together.22. The connector system of claim 21, wherein said at least one of saiddifferent receptacles comprises a first end of said adapter, said secondopening of said at least one of said different receptacles permits saidferrule of said mating plug inserted into said first end of the adapterto abut a ferrule of a second plug inserted into a second end of theadapter.
 23. A connector system comprising: a set of optical plughousings, each plug housing defining an opening configured toaccommodate the disposition of a ferrule therein, said each plug housinghaving a front face, said each plug housing defining a first keyingelement at least partially on said front face, said first keying elementof said each plug housing in said set of optical plug housings beingdifferent; a set of optical receptacles, each receptacle having anopening to receive said each plug housing, said each receptacleincluding a ferrule guiding portion having at least one ferrule guidingsurface to assist in positioning said plug ferrule upon insertion intosaid each receptacle, said ferrule guiding surface being disposed withinan interior of said each receptacle on a projection that defines asecond keying element, said second keying element of said eachreceptacle being different and being adapted to cooperate with saidfirst keying element of one and only one plug housing of said set ofoptical plugs housings such that said each receptacle of said set ofoptical receptacles mates with only one plug housing of said set ofoptical plug housings, wherein said each plug housing and said eachreceptacle having first and second keying elements that cooperate are amating pair; and wherein said each plug housing and said each receptacleof said mating pair are marked with a matching visual identificationdifferent from plug housings and receptacles having different first andsecond keying elements.
 24. The connector system of claim 23, whereinsaid ferrule guiding portion in said each receptacle includes fourdiscrete ferrule guiding surfaces, each of said ferrule guiding surfacesbeing positioned adjacent and facing a surface of said plug ferrule uponinsertion of a mating plug into said each receptacle.
 25. The connectorsystem of claim 23, wherein said second keying element on said eachreceptacle extends from an inner surface of said each receptacle and isset back from a front face of said each receptacle.
 26. The connectorsystem of claim 23, wherein said second keying element in said eachreceptacle is a key and said first keying element on said eachreceptacle is a slot.
 27. The connector system of claim 23, wherein theprojection in said each receptacle includes at least one radiused orchamfered corner to help guide said plug ferrule inserted into thereceptacle.
 28. The connector system of claim 23, wherein said each plughousing has an outer periphery, and wherein said first keying element onsaid each plug housing is defined at least in part on said front faceand said outer periphery of said each plug housing.